An indoor unit of an air conditioner is known that comprises a ventilation fan that generates a flow of air, and a heat exchanger that exchanges heat with the air that passes therethrough, and that conditions air (i.e., cooling and heating) by blowing heat exchanged air into an indoor space; in addition, it is known with such an indoor unit of an air conditioner to provide overlapping heat exchanger layers that have different areas. For example, Japanese Published Unexamined Patent Application No. H10-205877 recited below discloses an auxiliary heat exchanger that has a dimension smaller than the width dimension of a heat exchanger and that is provided so that it overlaps part of that heat exchanger.